how to fix my carousel controls and indicators

i have a problem on my carousel using controls and indicators , which does not make my photos slide through other pictures , the only picture i only see is the one you marked as active . hope you help me guys thanks .

hope you help me figure out the prob

                <div id="example" class="carousel slide" data-ride="carousel">
                    <ul class="carousel-indicators">
                        <li data-target="#example" data-slide-to='0' class="active"></li>
                        <li data-target="#example" data-slide-to='1'> </li>
                        <li data-target="#example" data-slide-to='2'> </li>
                        <li data-target="#example" data-slide-to='3'> </li>
                    </ul>
                    <div class="carousel-inner">
                        <div class="carousel-item active"> <img src="/setup/img/portfolio.jpg" alt="port" class="d-block w-100 height-100"></div>

                        <div class="carousel-item"> <img src="/setup/img/mypic.jpg" alt="ports" class="d-block w-50"></div>

                        <div class="carousel-item"> <img src="/setup/img/code.jpg" alt="port1" class="d-block w-50"></div>

                        <div class="carousel-item"> <img src="/setup/img/about.jpg" alt="port2" class="d-block w-50"></div>
                    </div>
                    <!-- controls-->
                    <a href="#example" class="carousel-control-prev" data-slide="prev">
                        <span class="carousel-control-prev-icon"></span>
                    </a>
                    <a href="#example" class="carousel-control-next" data-slide="next">
                        <span class="carousel-control-next-icon"></span>
                    </a>
                </div>
            </div>

i expect to be able to use my controls or even even just the indicators .